1. Field of the Invention
The present invention relates to hydraulic pump/motors uniquely arranged on a common shaft, including an apparatus for simultaneously changing the displacement of more than one pump/motor.
2. Description of the Related Art
Hydraulic pump/motors such as bent-axis piston machines, are used for a variety of applications in numerous industries, including the marine, automotive and aerospace industries. Such pump/motors are commercially available from a number of manufacturers, for example, Bosch Rexroth Corporation, headquartered in Hoffman Estates, Ill.
In some applications, such as hydraulic automotive transmissions, it is desirable to have a set of opposing bent-axis piston machines on a common input/output shaft. Conventional assemblies with two or more pump/motor units arranged on a common shaft use one or more sets of bearings in hard contact with drive plates of the pump/motors to bear and transmit axial and radial forces generated by the pump/motors. The forces may then be transferred from the bearings into a common housing for load cancellation. As each pump/motor may generate up to and beyond 10,000 pounds of axial force at its lowest displacement, the bearings experience high loads and friction, reducing the efficiency of the system and life of the bearings. The bearings must therefore be sufficiently large to withstand these loads, adding to the weight and cost of such systems.
Due to these and other limitations, Applicant believes that there is a need for a new and improved system for providing two or more opposing pump/motors on a common shaft. Applicant further believes that there is a need for a system for simultaneously changing the displacement of two or more pump/motors. The present invention provides such systems.